An epoxy resin is widely used in fields of adhering, casting, sealing, laminating, molding, coating, and the like from the standpoints of its excellent cured properties and easy handling property.
In general, epoxy resins obtained by reacting a compound having an active hydrogen, such as a phenol compound, an amine compound, or a polycarboxylic acid with epihalohydrin are widely used as the epoxy resin. Further, modified epoxy resins obtained by further reacting the above-described epoxy resin with a compound having an active hydrogen to thereby control the molecular weight or impart additional functions to the epoxy resin are also widely used.
For example, the epoxy resin and a polyhydric phenol compound are reacted to increase a molecular weight of the epoxy resin, whereby a flexibility thereof can be improved and flow property thereof at molding can be controlled. Further, a flame retardancy can be imported to the epoxy resin by reacting the epoxy resin with a brominated phenol compound to thereby introduce a bromine atom into the epoxy resin.
Recently, various properties required in resin material become severe with the progress of various techniques and change of use environment, and in particular, improvement in moisture resistance or the like is an important problem in various use fields such as adhering, casting, sealing, molding, laminating, coating, and the like. Further, where the epoxy resin is used in an electrical field, improvement in electrical properties is also an important problem. However, modified epoxy resins generally used recently are not sufficiently satisfied with the required properties.
That is to say, modified epoxy resins obtained by a production process comprising reacting an epoxy resin widely used with a compound having an active hydrogen, such as a phenol compound, an amine compound, or a polycarboxylic acid do not have sufficient moisture resistance and electrical properties.
In the conventional production method comprising reacting the epoxy resin with a compound having an active hydrogen, a hydroxyl group having a high polarity is formed by a reaction between an epoxy group and an active hydrogen group, resulting in deterioration of the moisture resistance and the electrical properties of the modified epoxy resin.
Various improvements such as change of skeleton, modification, and the like have been attempted in conventional production processes. However, unless the above-described basic problems are overcome, modified epoxy resins having sufficiently satisfactory moisture resistance and electrical properties cannot be produced.
One object of the present invention is to provide a modified epoxy resin which gives a cured resin having excellent moisture resistance and electrical properties. Another object of the present invention is to provide a process for producing the modified epoxy resin. Still another object of the present invention is to provide an epoxy resin composition which gives a cured resin having excellent moisture resistance and electrical properties.